The present invention relates to a process to upgrade light paraffins, preferably C2-C5, to high-octane gasoline. The process is particularly applicable to the upgrading of iso-paraffins, which are abundantly found in Natural Gas Liquids (NGL) and tight oils (produced from shale or sandstone), as well as fractions from various refining and/or chemical streams.
With the increasing production of shale gas and tight oils, the supply of light paraffins (e.g., C.2-C8, especially C2-C5 paraffins) is increasing at an unprecedented rate in the North America region; a large fraction (up to 30%) of NGL, for example, is C4/C5 paraffins. At the same time, demand for C4/C5 molecules is decreasing due to a number of factors: (1) steam crackers switching feed from light naphtha to ethane; (2) shrinkage of the gasoline pool in the North American market; and (3) a potential mandate for gasoline Reid Vapor Pressure (RVP) reduction. Although diluent use of C5s for heavy crude is predicted to grow somewhat, the supply of C4s/C5s is quickly outpacing demand and the imbalance will become worse with time.
Profitable dispositions for ethane (e.g., cracking to make ethylene) and propane (e.g., dehydrogenation to make propylene) exist. Upgrading C4/C5 paraffins to higher value and large volume products, while desirable, remains challenging. Conversion of C4/C5 paraffins to heavier hydrocarbon products such as gasoline, kerojet, diesel fuels, and lubricant basestocks would provide a large volume and higher value outlet to help alleviate the excess of light ends in the North American market. But there is no current commercial process directly converting light paraffins to heavier hydrocarbons such as these. Conventional upgrading practices first convert light paraffins to olefins via cracking or dehydrogenation, followed by olefin chemistries such as oligomerization or polymerization, alkylation, etc., to build higher molecular weight molecules. A number of technologies are known to convert light paraffins to aromatics such as BTX (benzene, toluene, and xylenes), including the Cyclar™ process developed by UOP and the M2-Forming process developed by Mobil Oil Corporation.
Currently, modern automobile gasoline engines require high octane fuel, and the demand for high octane gasoline is expected to continue to grow. Current high octane molecules from refining processes include aromatics, oxygenates, and alkylates. Current gasoline molecules from refining processes, with the exception of toluene, have a road octane number less than 110, such as the following typical road octane values: iso-butane 99.8; 2,3-dimethylbutane 100; 2,2,3-trimethylbutane 107.1; C8 trimethyls 101.9; benzene 100.8; toluene 110.7; C8+ aromatics 108.5-96; MTBE 106.2; TAME 106.5; and ethanol 100.4. Although aromatic molecules typically offer high octane, particulate emissions are a concern. Oxygenated high octane gasoline molecules such as ethanol have lower energy content (e.g., ethanol has ˜82% of the volumetric energy content of gasoline) and can cause compatibility problems at high blending ratios. There is no commercial process to produce non-aromatic, non-oxygenated molecules with higher than 110 road octane. As such, there still remains a need for a process for producing higher octane, non-aromatic, non-oxygenated gasoline molecules, especially a process using readily available feedstocks, such as light paraffins.